A conventional biosensor test strip 10 as shown in FIGS. 1 and 2 comprises: a cover plate 11, a spacer plate 12 and a base plate 13 combinably superimposed to form the test strip 10. The base plate 13 is printed thereon with a first electrode 131, a second electrode 132, a conducting electrode 133, and a reference electrode 134. A first working electrode 131a is formed on a terminal portion of the first electrode 131; while a second working electrode 132a is formed on a terminal portion of the second electrode 132. A reaction zone 135 is defined between the first working electrode 131a and the second working electrode 132a, having a biological reagent 136 (such as an enzyme) is provided in the reaction zone 135. Upon feeding a user's liquid sample into the reaction zone 135, the sample will be reacted with the reagent 136 electrochemically to produce an impedance signal across the first and second electrodes 131, 132 to be converted into a readable data (such as a concentration of blood glucose, blood lipid, etc.) to be displayed on a measurement apparatus or meter. Such an impedance signal from the first and second electrodes 131, 132 may be commensurate with the reference electrode 134.
However, such a conventional test strip 10 has the following drawbacks:    1. The reaction zone 135 is an open area without being confined or limited by any wall, thereby easily spreading or losing the liquid sample nearby to cause measurement errors and affect measurement precision.    2. Larger quantity of the user's liquid sample is required in order to provide or compensate sample enough to be efficiently sensed in the “open” reaction zone 135. This may scare the user or patient, making him or her uncomfortable by sucking much blood as required.    3. Whenever feeding the liquid sample into the reaction zone 135, the sample must be penetrated capillary through an aperture between the cover plate 11 and the electrode 132a to “reach” the reaction zone 135 finally. However, there is no means for limiting or guiding the liquid sample to be smoothly penetrated into the reaction zone (i.e., the slim area between the two electrodes 132a, 131a). The liquid sample may be spread sidewardly capillary, with only a partial “stream” flowing into the reaction zone. So, it requires further means or method to ensure (double-check) the liquid sample to be safely led into the reaction zone, causing measurement inconvenience or wasting related resources.
Another prior art of U.S. Pat. No. 6,939,450 disclosed a biosensor including a device having a flow channel (114) into which a liquid sample is drawn therein and flows therethrough by means of capillary attraction.
However, such a device still has the following drawbacks:    1. Once the liquid sample is introduced into the sensor area and reaction site, the liquid sample may flow capillary through the flow channel (114) lengthwise, or may spread sidewardly, without being stably retained within the reaction site to be reacted with the reagent, thereby easily causing examination error and affecting test precision.    2. Larger quantity of liquid sample, such as a patient's blood, is required (even unwelcome) in order to compensate the capillary or spreading loss when introduced onto the test strip.    3. A flow-terminating interface (118a), such as openings (122a), should be provided to form a barrier to disrupt the force of capillary attraction that causes the liquid to flow in the flow channel. Such a flow-terminating interface may increase the production complexity and cost of the biosensor strip, and may also deteriorate the product quality since the plural openings (122a) may weaken the product strength.
The present inventor has found the drawbacks of the prior arts, and invented the present sample-retainable biosensor test strip.